Measuring thermal conductivity in freezing and thawing soil using the soil temperature response to heating

Abstract

The thermal conductivity of the thin seasonally freezing and thawing soil layer in permafrost landscapes exerts considerable control over the sensitivity of the permafrost to energy and mass exchanges at the surface. At the same time, the thermal conductivity is sensitive to the state of the soil, varying, for example, by up to two orders of magnitude with varying water contents. In situ measurement techniques perturb the soil thermally and are affected by changes in soil composition, for example through variations in thermal contact resistance between sensor and soil. The design of a sensor for measuring the temperature of the soil rather than the axial heating wire temperature has consequences for the modeling of heat flow. We introduce an approximation of heat flow from a heated cylinder with thermal contact resistance between the cylinder and the surrounding medium. This approximation is compared to the standard line source approximation, and both are applied to data measured over a one-year period in northern Alaska. Comparisons of thermal conductivity values determined numerically using the line source solution, line source approximation and the analytical form of the heated cylinder model fall within 10% of accepted values, except for measurements made in pure ice, for which all methods of calculation under-predicted the thermal conductivity.Field data collected from a complete freeze-thaw cycle in silty clay show a seasonally bimodal apparent thermal conductivity, with a sharp transition between frozen and thawed values during thaw, but a three-month transition period during freezing. The use of soil composition data to account for changes in heat flow due to the effect of latent 2 heat during phase change results in a relationship between soil thermal conductivity and temperature.

Evaluation of the heat pulse probe method for determining frozen soil moisture content

“…During the measurements, the heating needle releases a short heat pulse and the detecting needles measures the temperature T (°C) changes some distance from the heater. Heat propagation from the line source can be represented by the heat conduction equation in radial coordinates [ Patankar , 1980; Overduin et al , 2006]: where r is the radial distance from the center of the heating needle, b is the radius of the heating needle, t is time after heating start (s), and C and λ are soil volumetric heat capacity (J m −3 °C −1 ) and thermal conductivity (J °C −1 m −1 s −1 ), respectively. A constant heat source q′ (J m −1 s −1 ) is applied at r = b during the heat pulse duration t 0 (s) as a flux boundary to in order to solve the temperature at time t and distance r .…”

Evaluation of the algorithms and parameterizations for ground thawing and freezing simulation in permafrost regions

“…Approximately 35% of the earth's surface is subject to seasonal freezing and thawing, with 26% estimated to be underlain with permafrost [ Williams and Smith , 1989]. Because the thermal and hydraulic properties of frozen soils are distinct from those of the same soil in the unfrozen state [ Lachenbruch et al , 1982; Farouki , 1986; McCauley et al , 2002; Quinton et al , 2005; Overduin et al , 2006], ground thawing and freezing processes strongly influence the surface energy balance and hydrological processes [ Woo , 1986; Williams and Smith , 1989]. The latent energy consumed (released) during thawing (freezing), along with changes in soil thermal properties, greatly alters the surface and subsurface energy partitioning patterns during the unfrozen, frozen and transition periods in permafrost soil [ Boike et al , 1988; Gu et al , 2005; Quinton et al , 2005].…”

“…Previous studies have prescribed surface forcing [e.g., Jumikis , 1977; Goodrich , 1978, 1982b; Lunardini , 1981; Riseborough , 2004], or prescribed soil moisture and thermal properties [e.g., Goodrich , 1978, 1982b; Romanovsky et al , 1997; Hinzman et al , 1998; Li and Koike , 2003; Ling and Zhang , 2004; Woo et al , 2004]. For example, in the validation of a modified Stefan's algorithm, a 5% unfrozen water content was used for six field sites ranged from polar desert to agricultural land [ Woo et al , 2004], while observed values ranged from 0% in coarse‐grained mineral soil to more than 20% in certain organic or clay soils [ Anderson and Tice , 1972; Nakano and Brown , 1972; Romanovsky and Osterkamp , 2000; Quinton et al , 2005; Overduin et al , 2006]. Most existing evaluation/validation studies of GTFD simulations only included single algorithm [e.g., Goodrich , 1978; Fox , 1992; Hinkel and Nicholas , 1995; Hinzman et al , 1998; Cherkauer and Lettenmaier , 1999; Quinton and Gray , 2001; Zhang et al , 2003; Woo et al , 2004; Hayashi et al , 2007], and only a few compared different algorithms [e.g., Romanovsky et al , 1997; Luo et al , 2003].…”

Field Test and Sensitivity Analysis of a Sensible Heat Balance Method to Determine Soil Ice Contents

“…Their numerical study showed that the SHB method could determine ice content as a function of depth and time at the centimeter scale if accurate thermal properties were obtained. However, the feasibility of the SHB method for soil freezing and thawing is unknown because of the difficulties in measuring soil thermal properties in partially frozen soils (Putkonen, 2003; Overduin et al, 2006; Ochsner and Baker, 2008; Watanabe et al, 2010). Further evaluation of the SHB method for partially frozen soil is warranted including, in particular, evaluation of the required HP measurement inputs under these challenging conditions.…”